Radio 1's excursions around the country used to mean the dreaded Roadshow, where audiences would endure guess-the-mileage competitions for a glimpse of Tony Blackburn. Nowadays, the annual free Big Weekend takes pop's biggest names to such outposts as Carlisle, where none other than Lady Gaga is making her only UK festival appearance this year.

R1BW has a more lightweight pop feel than most festivals. Tiny hot pants (sported by Jessie J and Ellie Goulding, and thousands in the audience) are the weekend's fashion must, in clear defiance of the weather. Even the unsigned bands stage features lip-synching and gyrating dancers, while 1FM jocks make Smashie and Nicey comments to big up mediocre acts.

Sometimes, it feels as if the gulf between the nation's favourite and the real world is as wide as ever. Kentucky's Stooges-like Cage the Elephant are "one of the most exciting bands to emerge this year" – news to anyone who's followed them since 2008. However, there is something for everybody. Early comers who beat the two-mile tailback are rewarded by a terrific secret opening set from indie titans Arctic Monkeys.

Rock is catered for by a brutally – if hoarsely – rocking Foo Fighters. DJ trio Swedish House Mafia prove a hit despite initially forgetting to press their "on" button. The biggest crowds flock to the genre-hopping acts who can unite the tribes – rap/soul hybrid Plan B and an anthemic Black Eyed Peas, whose "human zebra" dances are enough to make anyone suspect they'd wandered into Glastonbury and been given some bad acid.

Sunday brings a washout and the irony of the Strokes headlining the In New Music we Trust stage after a decade on the block. Their guitars sound zippy and effervescent but at times singer Julian Casablancas seems to be performing an entirely different song to his bandmates. There's a mass exodus to see Lady Gaga, possibly the only time the world's biggest music star will appear in a soggy Cumbrian field. A 20-minute delay heightens the expectation. Will she wear the meat dress, or make her entrance in a giant egg, like at the Brits?

There are gasps of "She's dead!" as the enigmatic star finally appears – in a coffin, clad in a PVC catsuit, and sporting a prosthetic pregnant belly for opener Born This Way. This early triumph aside, life mimics Spinal Tap as the strangely breathless 25-year-old chooses this moment to unveil her own personal jazz odyssey. There are interminable trumpet solos, wobbly scat singing, a Nat King Cole ballad amended as an "ode" to Kate Middleton and Prince William, and so much squawking you can't hear fans' jaws hitting the floor.

A big-lunged ballad about her grandfather appears to make the singer cry, although perhaps not as much as the television programmers broadcasting it live on BBC3. New song The Edge of Glory turns into a Hey Jude-style singalong, but having virtually ignored her hits, a determined Just Dance and Judas arrive too late to save the day. It's hard to remember a major star wrong-footing an audience this much since David Bowie killed off Ziggy Stardust. However, Bowie took his fans with him; a good chunk of Gaga's "little monsters" are drifting to the exit.